The components of most mining and processing equipment that are subject to wear (eg slurry pumps, cyclones and crushers) are produced from wear resistant white cast iron alloys.
Castings of these white cast iron alloys have high wear resistance and provide good service life for process equipment that is subject to erosion and abrasion wear.
Australian Standard 2027 describes inter alia the following two families of wear resistant white cast iron alloys:                (a) high chromium white cast iron alloy, eg 27% Cr; and        (b) chromium-molybdenum white cast iron alloy, eg 20Cr-2Mo and 15Cr-3Mo.The microstructures of all these white cast iron alloys consist of two phases, namely:        (a) M7C3 carbides (where M=Fe, Cr, Mn, Mo), which have a hardness of 1200-1500 HV; and        (b) ferrous matrix that consists of one or more of the following structures (i) a saturated solution of austenite which is metastable at room temperature, (ii) solute-depleted austenite containing secondary carbide precipitates and is destabilised at room temperature (iii) destabilised, retained austenite partially transformed to martensite and (iv) destabilised, retained austenite wholly transformed to martensite.        
The wear resistance of these white cast iron alloys is due to (a) the presence of the extremely hard M7C3 carbides and (b) the presence of a hard martensitic structure in the ferrous matrix.
It is essential to avoid the formation of pearlite in the ferrous matrix in these alloys during cooling after heat treatment in order to ensure adequate wear resistance in service.
It is a common practice to subject white cast iron alloys to an intermediate annealing process to deliberately form pearlite in order to soften the alloy for machining purposes. However, the machined white cast iron alloys are then subjected to a final heat treatment process to harden the alloys prior to service.
The ferrous matrix of AS2027, Grade 27% Cr (high chromium) white cast iron alloys can be readily hardened by forming martensite in the ferrous matrix during air cooling after heat treatment. One of the functions of the chromium in the alloys is to suppress the formation of pearlite during cooling from elevated temperatures.
However, white cast iron alloys containing lower chromium contents, eg 20Cr-2Mo and 15Cr-3Mo, require the addition of molybdenum and/or nickel to suppress the formation of pearlite on cooling after heat treatment, particularly in heavy section castings, ie castings greater than 10 cm thick. However, molybdenum and nickel are each expensive alloying elements and add substantially to the material cost of white cast iron alloys.